1. Field of the Invention
The invention relates to a laser welding method and an engine cooling structure of which members are welded by laser welding.
2. Description of Related Art
Welding with the use of an irradiated laser beam, different from arc welding, or the like, produces a smaller amount of slags, and may also be applied to welding of fine members and connected portions of thin sheet materials, so various suggestions have been made (for example, Japanese Patent Application Publication No. 2000-90893 (JP 2000-90893 A), and the like).
In JP 2000-90893 A, by reducing the material thickness of connected portions or providing cutouts at the outer edges of the respective connected portions, a battery case and a lid, each are made of aluminum having a low absorption of laser beam or an aluminum-based alloy, are welded to each other with the use of a low-power laser beam.
Incidentally, not limited to members made of aluminum or an aluminum-based alloy, welded members that are object to be welded by laser welding with the use of a laser beam have a variety of its dimensions, application portions, and the like, so it may be difficult to reduce the material thickness unlike a battery case. In addition, even when the absorption of a laser beam is increased by the cutouts of the outer edges of the connected portions, there is a limit of a depth at or below which melting occurs due to a laser beam (hereinafter, the depth is termed laser welding depth where appropriate). Therefore, in order to increase the reliability and strength of laser welding, there is a need to increase the laser welding depth.
In recent years, aluminum or an aluminum-based alloy is ordinarily used for a key component of a machine structural component; nevertheless, such a key component requires a mechanical strength in many cases. However, in laser welding, the reliability of ensuring the strength of welding is low due to a shallow laser welding depth, so application of laser welding to a key component has not been increasing so much.